Telecommunications networks are subject to failure and must be restored after failure. Two competing methodologies have evolved to devise plans to restore telecommunications networks after failure: pre-plan and dynamic route generation. In the pre-plan methodology, restoral routes are generated for every traffic route within the network prior to network failure. Plans are then created to implement the restoral routes. These plans are known as "pre-plans," and each pre-plan contains a set of commands for issuance to restoration network devices to activate the restoral routes. "Restoration network devices" are devices, such as digital cross connects (DXCs), that are used to restore traffic on the network in the event of network failure.
The pre-plan methodology has the benefit of generating optimal restoral routes. In general, all possible restoral routes ("pre-plans") within a given a cost limit are generated for each traffic trunk, and the best (i.e., lowest cost) restoral route among those generated is selected for use in restoring the network. A major disadvantage of the pre-plan methodology is that it takes a long time to generate a batch of pre-plans for an entire telecommunications network. Moreover, given that network topology is generally very dynamic, there is a great likelihood that the pre-plans are quickly outdated after generation.
In the dynamic route generation methodology, a restoral route is generated for an impacted traffic route in real time in response to the network failure. Dynamic route generation is also referred to as "real time restoration." Dynamic route generation generally places a cost limit on possible restoral routes and only generates the routes that fall within the cost limit. Typically, the cost limits used in pre-plan route generation are substantially higher than those used in dynamic route generation. The low cost limits employed in dynamic route generation ensure that very few routes are generated and considered; hence, increasing the speed with which a restoral route is generated.
One advantage of the dynamic route generation methodology is that it is very fast and uses current topology data. There is no need to generate a massive set of pre-plans as in the pre-plan methodology. A disadvantage suffered by the dynamic route generation methodology is that it often selects sub-optimal restoral routes for the sake of speed.